<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <input type="text" id="new">
    <select id="num">
        <option value="+">+</option>
        <option value="-">-</option>
        <option value="*">*</option>
        <option value="/">/</option>
    </select>
    <input type="text" id="new2">
    <span onclick="black()">=</span>
    <span id="wk"></span>
</body>
<script>
        function black() {
            let n = document.getElementById('new').value;
            let num = document.getElementById('num').value;
            let new2 = document.getElementById('new2').value;
            document.getElementById('wk').innerHTML =  eval(n+num+new2);
        }
    </script>
</html>